Tritium (T) is dissolved in normal water (H2O) as a tritium ion (3T+) and water isotope isomers (T2O, THO). The tritium ion is an isotope of a hydrogen ion (1H+) and a radioactive element which emits β-ray (electron beam) and has a half-life period of 12.3 years. In addition, the tritium ion (3T+) has chemical properties similar to those of a hydrogen ion (1H+) so as to have a property that the tritium ion (3T+) remains in the body by being exchanged with the hydrogen ion which constitutes the DNA in the body of a living being. For this reason, the tritium ion is harmful as it can be a causative agent of internal exposure.
The natural abundance of tritium is a significantly small amount (proportion of one per 1×1018 of hydrogen atoms), but tritium is artificially produced in a fission-type nuclear power facility or a nuclear fusion reaction facility. For this reason, the limit of waste water concentration by the laws and regulations of Japan is defined as 60,000 Bq/L (60 Bq/mL) as the limit value of radioactive concentration derived from tritium per 1 liter of the sample water in the notification to define the dose limit or the like on the basis of the provisions of the regulations on the establishment of commercial power reactor, the operation, and the like.
Usually, the difference in the physical properties such as the boiling point and the mass between water (H2O) and water isotope isomers (T2O, THO) that is different from water in order to separate tritium in water. These methods of the prior art are described, for example, in Vasaru, G. Tritium Isotope Separation 1993, CRC Press, Chap. 4-5, Villani, S. Isotope Separation 1976, Am. Nuclear Soc., Chap. 9, Gould, RF Separation of Hydrogen Isotopes 1978, Am. Nuclear Soc., Chap. 9, and the like.